1. Field of the Invention
The present invention relates to a sputtering apparatus. More particularly, the present invention relates to a sputtering apparatus that generates a magnetic field in front of a target while forming a metal layer on a substrate.
2. Description of the Related Art
Recently, the design of semiconductor devices has rapidly progressed as the use of means, such as a computers, for information processing becomes more wide-spread. In particular, this progress has required semiconductor devices to function at higher operating speeds, and to have larger storage capacities. In order to satisfy such requirements, semiconductor devices with increased density, reliability, and response time are under development. Accordingly, design requirements of a metal layer, for use in forming a wiring pattern in a semiconductor device, are becoming stricter.
The metal layer is generally formed by sputtering a metal, such as titanium, titanium nitride, aluminum, and the like, from a target onto a substrate. Research and development of sputtering methods for forming such metal layers has concentrated on improving the step coverage of the metal when deposited over a fine structure and improving the uniformity of the thickness of the metal layer when formed over a relatively large area on the substrate.
In order to perform sputtering most effectively, a magnetic field is generally employed. The use of a magnetic field allows the very desirable process conditions of low pressure and high density plasma to be achieved. Under these conditions, the particles sputtered from the target travel with a high degree of linearity. As a result, the step coverage is good. In addition, an element that generates the magnetic field is rotated to effectively control the behavior of the sputtered particles. Thus, uniformity in the thickness of the metal layer can be achieved in addition to the good step coverage. Therefore, the technique of using a rotating magnetic field to form a metal layer by sputtering has recently gained attention.
For instance, sputtering methods using a magnetic field are disclosed in U.S. Pat. No. 6,228,236 (issued to Rosenstein et al.), U.S. Pat. No. 6,183,614 (issued to Fu) and U.S. Pat. No. 4,995,958 (issued to Anderson et al.), Japanese Patent Laid-open Publication Nos. Hei 8-74051 and Hei 9-310174, and Korean Patent Laid-open Publication No. 98-65920.
However, despite the use of a magnetic field, the sputtering methods disclosed in the publications listed above may produce defects. In particular, the methods frequently generate a defect during the formation of a metal layer when the critical dimension of the semiconductor device is no more than 0.15xcexc or when the metal layer is formed on a patterned layer whose opening(s) has an aspect ratio of 5:1 or more. This defect, produced by a local corrosion of the target, may take the form of, for example, an overhang around the opening.
FIG. 1 is a graph of the corrosion profile of a target when using a sputtering apparatus having a magnetic field-generating member of the type disclosed in U.S. Pat. No. 4,995,958. The target corrosion depth in FIG. 1 is in millimeters.
Referring to FIG. 1, when a titanium layer is formed under a pressure of 5 mTorr, the corrosion at the central portion of the target is more severe than at the periphery of the target. Therefore, it is difficult to obtain a metal layer having a good step coverage and a uniform thickness using this method.
FIG. 2 is a graph of the corrosion profile of a target when using a sputtering apparatus having a magnetic field-generating member of the type disclosed in U.S. Pat. Nos. 6,228,236 and 6,183,613. Again, the target corrosion depth is in millimeters. In addition, the plot using the symbol xcex94 represents the corrosion profile of a target when employing a magnetic field-generating member of the type disclosed in U.S. Pat. No. 6,228,236. On the other hand, the plot using the symbol ▪ represents the corrosion profile of a target when employing a magnetic field-generating member of the type disclosed in U.S. Pat. No. 6,183,614.
Referring to FIG. 2, when a titanium layer is formed under a pressure of 5 mTorr using either of the apparatuses disclosed in U.S. Pat. Nos. 6,228,236 and 6,183,613, the corrosion at the central portion of the target is more severe than at the periphery of the target. Therefore, it is difficult to obtain a metal layer having a good step coverage and a uniform thickness.
Nonetheless, various ways have been proposed to improve the step coverage or uniformity in the thickness of a metal layer formed by sputtering. For example, U.S. Pat. No. 6,274,887 (issued to Yamazaki et al.) discloses an example of a sputtering apparatus that includes a collimator. On the other hand, U.S. Pat. No. 6,121,134 (issued to Burton et al.) discloses an example of a sputtering technique employing an LTS (long throw sputter) method in which the distance between the target and the substrate is kept at least 170 mm.
Although the use of a collimator results in an improved step coverage of a titanium layer formed under a pressure of 5 mTorr, the sputtering rate of the titanium is significantly decreased. The sputtering rates according to the kind of collimator used are illustrated in Table 1 below. In Table 1, the kind of collimator is classified by the unit size of a lattice thereof.
Table 1 shows that the sputtering rate is less when a collimator is employed. Also, as the lattice becomes smaller, the sputtering rate becomes lower. Thus, using a collimator lowers the productivity of the sputtering method. In addition, collimators also require maintenance and thus, their use increases the manufacturing costs.
Likewise, the LTS method can also be characterized as having a low sputtering rate. This is because the sputtered particles must traverse a relatively great distance. In fact, when the distance between the target and the substrate is increased from 50 mm to 250 mm, the sputtering rate of the metal layer is lowered by 70%. Accordingly, the LTS method is also characterized as having low productivity.
An object of the present invention is to obviate the aforementioned problems and limitations of the prior art. Accordingly, an object of the present invention is to provide a sputtering apparatus in which a low pressure and a high density plasma can be maintained, which performs sputtering with a high degree of productivity, and which can produce a metal layer having good step coverage and a uniform thickness.
Another object of the present invention is to provide a sputtering apparatus having a magnetic field generator that can produce a corrosion profile of the target optimal for forming a metal layer having good step coverage and a uniform thickness.
The sputtering apparatus of the present invention includes a sputtering chamber, a target disposed in the sputtering chamber, and a magnetic field generator having a magnetic field-generating part forming a magnetic enclosure having an opening therethrough. The magnetic field-generating part is located at the back of the target at a position offset from a vertical axis passing through the center of the target, with the opening in the magnetic enclosure located in the direction of offset, i.e., along a line extending diametrically from said vertical axis.
Accordingly, a magnetic field having a non-uniform distribution is produced at the front surface of the target, at a location confined between the central and peripheral portions of the target, to optimize the corrosion profile of the target. Therefore, a metal layer having a good step coverage and a thickness uniformity can be formed by sputtering conducted under a low pressure using a high density plasma. Furthermore, the metal layer can be formed with a high degree of efficiency.